1. Field of the Invention
This invention relates to information storage media and, more particularly, to high density magnetic information storage media which comprises a plurality of discrete islands of magnetic material.
2. Background of the Invention
Present day high density magnetic information storage media contain small magnetic grains, usually in a thin metallic film. In this media, it is usual for one information storage bit to be stored in a region of the film which contains a large number of magnetic grains and which is magnetized coherently in one of two preferred directions--usually referred to as "up" and "down," even though the actual direction of magnetization may not be perpendicular to the film or other form of media on which the magnetic grains are deposited.
The demands of high density information storage have led to magnetic grains in the metal films with dimensions as small as 100 to 150 .ANG. (10 to 15 nm) which, in turn, has resulted in a large number of grains, on the order of thousands or tens of thousands, being contained within each individual information storage bit. Nonetheless, the recording medium remains fundamentally granular and the grains have a large dispersion (by a factor of two) in size. This granularity leads to media noise in the magnetic switching process, which gets worse as the bit size, hence the number of grains in a bit, becomes smaller. Although an ideal medium (with a constant grain size and containing N number of particles in each bit) results in a signal-to-noise ratio proportional to (N).sup. 1/2, the actual practical situation is much worse because of the irregularity in particle size, particle packing and particle interactions due to exchange coupling and demagnetization fields. Present day commercial hard disk storage media have a bit density of roughly 100 Mb/in.sup.2. Today's technology reaches physical limitation at 10.sup.8 and 10.sup.9 Mb/in.sup.2.
From the above, then, it appears that the contiguous granular media approach provides significant limitations to pushing the media significantly farther in the direction of smaller bit size and higher areal density, and therefore the need is for a different approach to high density magnetic storage media.